The present invention relates to a method for manufacturing a press-on lid intended to be clipped onto a tubular container or a cup of any shape equipped with an outwardly rolled edge at its top end, the press-on lid consisting of a strip and of a pressed disk, and to a lid manufactured according to this method.
At the present time, mass-produced consumer products relating equally to the food industry, chemical industry and industrial industry, are packaged in packaging consisting of a number of materials and components. For several years, for ecological reasons, packagings made of readily recyclable materials, eliminating other materials such as plastics, metals (aluminum), etc. to the greatest possible extent, have been proposed.
The object of the present invention is to provide, for tubular packagings and cups equipped at their upper end with an outwardly rolled edge, a press-on lid which, once the membrane or protective inner seal sealing the upper part of the packaging has been removed, allows the packaging to be sealed sufficiently hermetically for the duration of its use, that is to say until the product contained has been used up. This characteristic also applies to packaging without a membrane or inner seal.
There are currently in existence packagings, for example for food products such as butter, margarine, yogurt, or alternatively cups containing a liquid beverage, and other products contained in containers of any size made of a recyclable material, for example cardboard. These containers are covered at their top by a lid clipped onto an outwardly rolled edge of the container thus allowing the container to be sealed as hermetically as possible fdferonce the protective membrane has been removed, until the product contained has been fully used up. This type of lid is essentially made of a plastic, which is satisfactory from the efficiency viewpoint, but not from the point of view of the recycling of waste and they are difficult to decorate. Attempts at using a recyclable material such as cardboard or the like have not proved satisfactory with respect to changes of temperature. The humidity alters the dimensions of the lid and it loses its effectiveness.
The object of the present invention is to provide a lid made of a recyclable material such as, for example, cardboard, making it possible to have effectiveness identical to that of a plastic lid in terms of the use of the lid once the protective membrane has been removed.
The method according to the invention is characterized by the following steps:
a strip is cut from a rigid and fibrous material equipped on one of its faces with an adhesive, the cut being made parallel to the fibers of the material,
a ring is formed on a form of a size equal to the internal dimensions of the lid, the length of the strip allowing the ends to be superposed around the form so that they can be sealed together,
a disk is cut from a rigid material in a shape that corresponds to the lid prior to pressing,
these are introduced into a two-stage tool, the disk being introduced into the upper part and the ring into the lower part,
a heated punch is introduced into the ring and the disk is pressed and sealed onto the ring by means of said punch and of a die of said tool, the nesting profile is formed at the end of the travel of the punch.
The advantages of the method are as follows:
the use of a strip cut in the direction of the length of the fibers avoids any change in dimensions of the skirt of the lid because it has been found that with fibrous products such as cardboard, the fibers do not lengthen but simply swell under the influence of temperature and moisture. Thus, the dimensions of the lid do not change even after residing in a damp cold environment, household freezer or refrigerator, for some time.
A prototype of a lid was produced with a catch using a single layer of a material, for example of cardboard or any other equivalent fibrous material equipped only on the inside with a film. This prevented the product from coming into contact with the cardboard. However, because of the moisture and because of the deformation after one or two uses, the lid no longer effectively closed the packaging.
Following this experience, a way of achieving a lid made of these same recyclable materials but having the efficiency of a lid made, for example, of plastic was realized. The aforementioned solution was satisfactory because effective closure of the packaging is achieved even after this lid has been opened and closed a great many times.
According to a first special embodiment, a catch is formed by expansion in the form of a groove open toward the inside of the lid.
According to another embodiment, the disk protrudes beyond the ring over its entire periphery, and so after sealing the protruding part of the disk is turned back through 180xc2x0 onto the interior wall of the ring and is smoothed and sealed. This construction is even more effective than the previous one and provides greater resistance to deformation as a result of moisture and temperature changes to which the packaging is subjected.
According to another variant of the invention, the rigid material is cardboard or paper.
According to another embodiment, the adhesive material is an adhesive activated by heat or by cold.
According to another variant, the width of the strip approximately corresponds to the distance between the end of the skirt of the lid and the catch.
According to another variant, the adhesive material is a film activated by heat or by cold.
According to another embodiment, the disk is equipped with a protective film to prevent the packaged product from coming into direct contact with this disk.
The invention also relates to a lid fabricated according to the method of the present invention.